promoting the use of effective vibration mitigation

LTCS Engineering

Mid-Yr Planning Meeting

June 2012 AASHTO T12 Meeting, OH 6-24-2014

Promoting the Use of Effective Vibration Mitigation Devices for

Traffic, Sign, and Lighting Structures in the Existing AASHTO Specifications

Persons Developing the Problem:

Carl Macchietto (Valmont) & Rich Christenson (UConn)

Problem Monitor: Hannah Cheng (NJDOT)

Submitted by: Norman McDonald (Iowa DOT)

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&uact=8&ved=0CAQQjRw&url=http://www.qvcc.edu/advising/transfer.asp&ei=lRWnU_LZLoqRyASnkYDwDA&bvm=bv.69411363,d.aWw&psig=AFQjCNFwapre4SYphsh4YmE4zQXwHA-9Xg&ust=1403545365808910

Traffic, sign, and lighting structures are characterized by high flexibility & low damping, prone to wind-induced vibration, and susceptible to fatigue and failure.

There have been many documented wind induced vibration occurrences, some causing structural failure.

These vibration occurrences are dependent on structure, site and specific wind conditions, and are difficult to predict

Introduction


Indiana – 1st Mode, Aluminum Lighting Pole


Watertown, SD – High Mast, 1st Mode


Canada – Bridge Mono-tube Sign Structure


Colorado – Cantilever Mono-tube Sign Structure


Galloping Traffic Signal Structure


Austin, Texas - Traffic Arm Failure


Denver, Colorado - High Mast Failure


Typical Parking Lot Light Pole Failure


AASHTO LTS Specifications

Support structures shall be proportioned

such that the wind-load-induced stress is

below the constant amplitude fatigue

threshold (CAFT) – Ensuring Infinite

Fatigue Life.

Certain load cases govern design – producing

overdesigned and expensive structural

members and critical connections

Specifications can result in inefficient structural

designs – a questionable use of resources



Cantilevered Sign and Traffic Signals

1. Galloping

2. Natural Wind Gusts

3. Truck-Induced Gusts

Non-cantilevered Sign and Traffic Signals

1. Natural Wind Gusts

2. Truck-Induced Gusts

High-Mast Lighting Towers (55’ and taller)

Design wind pressure includes natural wind, natural

wind gusts, and vortex shedding

Roadway Lighting Pole Structures (less than 55’)

Do not need to be designed for Fatigue


In lieu of designing to resist periodic galloping forces,

the AASHTO specifications suggest the use of

effective vibration mitigation devices for cantilever

traffic and sign structures.

The mitigation device should be approved by the

Owner, and based on historical or research verification

of its vibration damping characteristics.

The AASHTO specification makes no reference for the

allowance of effective vibration mitigation devices for

other fatigue load cases such as Truck, Natural Wind

Gusts, or High Mast; or for other Structure types such

as non-cantilevered Sign and Traffic Signal Structures.


Vibration Mitigation Devices

Owners rarely consider the use of

mitigation devices because:

It’s difficult for owners to reliably define how

effective a vibration mitigation device functions

The AASHTO Specifications gives no guidance

as to how to qualify or quantify the

effectiveness of a device


Research Objectives

Develop test procedure that can be followed by

traffic, sign, and lighting structure owners to

qualify particular mitigation devices as being

effective for specific structures and loading

conditions

Provide accompanying set of design procedures

to incorporate the added performance of the

vibration mitigation device into the design of the

structure

Develop recommendations to enhance AASHTO

Specifications


Research Phases and Tasks

Phase 1: Quantifying Performance of Vibration

Mitigation Devices

Phase 2: Identifying Test Procedures to Qualify

Mitigation Devices

Phase 3: Incorporate Effective Vibration

Mitigation Devices into Specifications

Research Period: 2 ½ years (30 months)

Recommended Funding: $400,000


Broader Impacts and Benefits

Owners can provide smaller, more efficient,

traffic, sign, and lighting structures

Improve public safety at reduced costs

Extend the life of new and existing traffic, sign,

and lighting structures

Get existing inventory compliant to current

AASHTO specifications

Spur innovation of new vibration mitigation

devices by making a clear path to implementation


Thank You


promoting the use of effective vibration mitigation

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